This invention relates generally to spark plugs, and, more particularly to spark plugs which increase the overall efficiency of combustion and reduce the amount of noxious emissions, particularly oxides of nitrogen (NOx) resulting from internal combustion engines.
Pre-combustion chambers (PCC's) are means for reducing exhaust emissions, particularly NOx, and for improving the performance and fuel economy of internal combustion engines. PCC's can be applied to gasfueled, spark ignited, reciprocating or rotary engines.
One of the most popular means of controlling NOx today is to increase the Air Fuel Ratio (AFR) of incoming gases to be combusted commonly referred to as lean burning. In lean burn engines, increasing AFR provides a greater mass of air to absorb the heat generated by a given mass of fuel, causing lower temperatures, and a slowing of NOx formation.
AFR's necessary to achieve desired low NOx levels require stratifying the cylinder charge by using a precombustion chamber to achieve consistent flame ignition. With PCC's and a very lean AFR, the extent of NOx control is much greater and is limited mainly by residual NOx attributable to richer pilot mixtures needed to ignite the leaner fuel.
The basic function of a PCC is to provide a nook or chamber where pilot or additive fuel can be combined with a portion of air to form a mixture consistently ignitable by a spark plug. The mixture when ignited provides the required energy to cause combustion of the very lean mixture within the main cylinder at the optimum time for efficiency and/or pollution control.
For consistent ignition the present day state of the art generally and erroneously holds that:
1. A PCC must contain a volume of between one and three percent of the minimum cylinder volume in order to provide sufficient ignition energy; PA1 2. The passageway between the PCC and the main cylinder needs to be sized to cause the ignited charge of the PCC to torch into the main cylinder with significant penetration; and PA1 3. The charge contained within the PCC must be of a near homogeneous mixture when ignited.
Spark plugs have been developed in the past to carry combustible gases into a cylinder. A mixture of gaseous fuel and air is supplied to the spark plug mixed in such a proportion, so as to be considered rich enough to ignite in the presence of a sufficient spark. The mixed pre-combustion gases are fed into a recessed area within the spark plug at its ignition end. Alternately, valving conduits can feed gaseous fuel into the recessed area, while other valving elements can supply air into the recessed area. Either the air or the gaseous fuel can be modulated to obtain a combustible fuel mixture. The combustible fuel can be ignited by a spark discharged from the spark plug. This sends a flame from the recessed area into the adjacent cylinder of the engine. Leaner fuel mixtures, normally not combustible by spark ignition, can be combusted as a result of the entering flame. The desirable results of such lean combustion are well discussed in U.S. Pat. No. 4,319,552 dated Mar. 16,1982, as well as other documents referenced therein.
The complexities of the valving conduits and related connectors and the required gaseous fuel/air modulation make this approach expensive and often times leads to poor results. This is true as the modulation of fuel and air cannot be easily and properly adjusted.
There is a tremendous potential interest, especially in the control of air emissions from automobiles, for a spark plug which is easy to install, does not require valving conduits for both air and gaseous fuel, and where the air and gaseous fuel can be easily modulated to bring about pre-combustion within a spark plug to ignite substantially leaner mixtures as desired.
The features identified as being desired for pre-combustion spark plugs are all provided by the present invention.